1. Field of the Invention
This invention relates generally to reinforced structural components and, more particularly, to reinforced structural composite castings for aircraft engines with parts made of titanium.
2. Description of the Prior Art
Presently, many high strength aircraft engine structural components are made of titanium or an alloy thereof. One such component is an aircraft gas turbine engine fan frame, particularly the struts thereon. Titanium, as opposed to aluminum or steel, is the material of choice because of its low density, high strength and high stiffness. However, recent aircraft design specifications demand lighter, more energy efficient and more powerful aircraft engines. Under present technology, aircraft engine structural parts made of cast titanium are at their limits with respect to strength, weight and stiffness characteristics.
In other fields of technology, cast metal structural parts have used cast-in-place structural inserts to strengthen and/or stiffen the part. See, for example, U.S. Pat. Nos. 4,651,631; 4,606,395; 4,852,630; 4,669,523 and 3,745,854. However, titanium has an extremely high melting temperature, on the order of in excess of 2900.degree. F. At these high temperatures, all known lightweight reinforcing materials degrade or melt. However, a proposal for titanium composite engine components submitted jointly by Howmet Corporation and General Electric Company to the U.S. Air Force in Proposal Number PRDA-NR-91-04-MLKT on Mar. 28, 1991 which proposed the possibility of using a cast-in-place insert for a titanium structural component. This proposal discusses a concept of casting a titanium strut around an insert made of a metal matrix composite made of metal and a ceramic reinforcing material. However, it is now believed, as a result of subsequent experimentation, that the reinforcing material in the structure of the proposal would normally degrade in this arrangement during the casting procedure due to the high temperature of the molten titanium.
Therefore, it is an object of our invention to provide a cast titanium structural component with a cast-in-place structural insert made of a dissimilar material that will not degrade during casting.
It is a further object of the present invention to provide an improved structural component for aircraft and/or aircraft engines.
It is yet a further object of the present invention to provide a process for making an improved structural component.